1. Field of the Invention
The present invention is related to a package of a constant-current supplying chip and a light-emitting diode (LED) lamp, and more particularly to a package of a constant-current supplying chip and an LED lamp driven by alternating current.
2. Description of the Prior Art
LEDs (Light-Emitting Diodes) are known to be compact, durable and power-saving and hence are widely applied for various kinds of illuminations and decorations. A prior art LED module driven by direct current requires a rectifying circuit or a power converter in order to convert an AC (Alternating Current) power source into a DC (Direct Current) power source. Therefore, a larger PCB (Printed Circuit Board) is required to accommodate the rectifying circuit or the power converter, which results in the prior art LED module driven by direct current being less compact and demanding higher cost.
Another prior art LED module driven by alternating current includes at least two LEDs connected in anti-parallel fashion, and resistors connected between the LEDs and the AC power source. In such configuration, the alternating current in the first half cycle drives the LED with a polarity in the same direction, and the alternating current in the second half cycle drives the LED with a polarity in the opposite direction. Compared to an LED module driven by direct current, an LED module driven by alternating current has a simpler circuit, and therefore has a smaller size and requires lower cost.
However, connecting an LED module directly to an AC power source may damage the LED by a surge current from the AC power source. Even though the surge current may be limited by a resistor of a higher resistance to provide a better protection, a higher percentage of power is being dissipated as heat by the resistor of such higher resistance, and the LED would be driven by a smaller current, resulting in the LED module having a lower luminous efficiency. Besides, since the current is varying with the voltage, the luminous intensity of the LED is harder to be controlled effectively.
In summary, providing a constant current to the LED so as to avoid the LED module driven by alternating current to be damaged by a surge current is highly desirable.